<form method="post" name="form_name" id="form_name" action="https://www.w3schools.com/comment.php">
<fieldset>
<legend>Title</legend>
<p>A brief explanation about what you would like to see entered.</p>
<textarea name="comment" form="form_name" maxlength='400' rows="8" placeholder='Character Limit: 400'></textarea>
</fieldset>
<input type="submit" value="Submit comment">
</form>
In addition you must decide what you want to do with the comments and how to process them one they are received via the post ($_POST) method at comment.php.
Roddy